2.1. Diseases Caused by Streptococcus pneumoniae
The pneumoccus (Streptococcus pneumoniae) is a gram-positive encapsulated coccus that usually grows in pairs or short chains. In the diplococcal form, the adjacent margins are rounded and the opposite ends slightly pointed, giving the organisms a lancet shape.
Pneumococci may be divided into serotypes based on the complex polysaccharides which form their capsules. 84 serotypes have been identified by exposure to type-specific antiserum, the Neufeld quelling reaction. All are pathogenic for human beings, but types 1, 3, 4, 7, 8, and 12 are encountered most frequently in clinical practice Types 6, 14, 19, and 23 often cause pneumonia and otitis media in children but are less common in adults (Austrian, 1983, in "Harrison's Principles of Internal Medicine", Petersdorf et al., eds., 10th Edition, McGraw Hill Book Co., New York pp. 918-922). Notably, the pneumococcus is one of the three primary pathogens responsible for pneumonia, sepsis, and meningitis in children (McMillan, 1982, in "Core Textbook of Pediatrics," Kaye et al., eds., Second Edition, J. B. Lippincott Co., Philadelphia, p. 498).